myoglobin and hemoglobin (1)

proteins must be correctly ______ to have proper _______

folded; fxn

ligand

any molecule that reversible binds to a protein

binding sites

specific sites on a protein that ligands bind at

characteristics of the binding site dictate ligand binding

-complimentary

• size

• shape

• charge

• hydrophobicity/hydrophilicity

the more a ligand is attracted the more

stabilized binding

myoglobin and hemoglobin are what type of proteins?

oxygen-binding proteins

where is myoglobin located in the body?

muscle

where is hemoglobin located in the body?

the blood

myoglobin ratio

1:1 1 myoglobin chain to 1 oxygen ligand

how many subunits are associated with hemoglobin?

4 and each allows O2 to bind

what structure is myoglobin?

tertiary

what structure is hemoglobin?

quaternary

where in the blood in Hb found?

in the RBCs

Hb center area

prosthetic group/disk that’s covalently attached

for the role of Hb O2 is loaded where?

the lungs

for the role of Hb O2 is unloaded where?

the tissues in the tissue cells

Mb uses O2 and does what?

binds and stores it

O2 binds in the mitochondria to get what?

energy

myoglobin

oxygen storage and transport protein in muscles

hemoglobin

oxygen delivery via blood vessels

myoglobin and hemoglobin common structural motif

• globin fold (8 alpha helices + heme)

• polypeptide chain folds around a prosthetic group(heme)

a heme is what type of ring

protoporphryin ring

heme group

protoporphryin ring + iron (Fe2+) bound

myoglobin used to be thought as a storage protein, but it’s really a…

oxygen diffuser that facilitates and increases oxygen diffusion to muscle (which is limited)

spherical (globular)

contains 8 helices A,B,C,D,E,F,G,H and bends bw helices AB, CD, EF, GH

what state must iron be in to be functional in a heme?

2+ state

O2 isn’t soluble in what solutions?

aqueous and that’s y we need hemoglobin

when is O2 solubility and transportability increased ?

when bound to a soluble carrier/ protein

what doesn’t reversibly bind to O2

AA side chains

what reversibly binds to O2

transition metals like Cu or Fe but we focus on Fe

describe the prosthetic group structure

protoporphyrin ring bound tightly to each subunit as part of tertiary structure and Fe bonds tightly to the ring

Fe2+ coordination sites

4 nitrogen’s of the protoporphyrin ring and a His residue

His F8

eight residue on the F helix (His 93)

what does His F8 do?

interacting with the iron in the heme

what does the His E7 do?

once O2 is bounds hydrogen bonds to the O2

what do Val E11 and Phe CD1 do?

hold the heme in place by preventing oxidation of Fe2 to Fe3 while creating a binding site for O2

binding of the O2 to the Fe2 heme complex alters what?

the electronic state of the complex changing the color from dark purple to scarlet

oxidation of the Fe2 to Fe3 prevents

binding of O2

Fe3 heme complex is what color if oxidized ?

brown which is known as methemyoglobin

what other ligands can bind to the Fe and what’s their affinity?

CO, NO, H2S with a higher binding affinity that’s toxic

Ka

association constant

Kd

dissociation constant; probability PL complex goes back to free form

what does Ka depend on?

P’s ability to bind to L to form PL and how L is available to bing; affinity and [L]

What does Kd depend on?

affinity and it based on the PL complex staying tg b4 PL releases L

if P has high affinity for L…

it’s less likely to go to the free form

if P had low affinity for L…

it’s more likely to go to the free form

Kd formula

[P][L]/ [PL]

relationship bw Kd magnitude and affinity

the lower the Kd, the higher the affinity

what does a small Kd value mean?

the bound form [PL] is favored

what does big Kd value mean?

the free form [P] is favored

full saturation

95% bound protein

full saturation

95% bound protein

multiplying fraction saturation by 100 does what?

converts it to percent saturation

carbon monoxide mild acute poisoning

light-headedness, confusion, headaches, vertigo, flu-like effects

carbon monoxide larger exposure poisoning

toxicity of central nervous system and heart, even death

Why does CO poisoning happen?

Mb and Hb efficiently bind to O2 preventing the drop off of it

how does CO like to bind?

vertically and not at an angle and the bound heme blocks CO bc of the distal his E7

once O2 receives electrons what happens?

it’s converted into H2O

CO binds tighter to bound or unbound heme?

unbound meaning w/out protein

what isn’t present in the unbound heme?

the distal his, his E7

Ka formula

[PL]/[P][L]

O with line thru it formula

binding sites occupied/total binding sites = [Pl]/[PL] + [P]

Myoglobin Ligand binding formulas

Kd= [Mb][O2]/[MbO2] or Kd=[Mb] • pO2/ [MbO2]

oxygen binding of myoglobin

YO2= [MbO2]/[Mb] + [MbO2] or YO2 = pO2/ Kd+pO2

fractional saturation for any ligand

O w/line thru it= L/Kd+L

And is equal to the conc. ligand at which the half sites are occupied also defined as…

p50

p50

oxygen pressure at which myoglobin is 50% saturated w O2

YO2 increases as Kd…

decreases

Mb has a p50 value of?

2.8 torr **** MEMORIZE

binding if considered weaker when?

when it takes a greater oxygen pressure (larger p50) to reach half saturation

alpha 2 beta 2 tetramer (4 myoglobin like polypeptides)

formed from a dimer of alpha beta protomers

how many oxygen burning sites does Hb have?

4

what does oxygen brining do to the hemoglobin structure?

alters it

Hb must be able to bind oxygen in the lungs

(high pO2, force Hb to bind O2)

Hb must be able to release oxygen in capillaries

(low pO2, Hb releases O2)

If Hb behaved like Mb (high affinity for O2, low Kd/p50)

very lil oxygen would be released in the capillaries; Hb’s p50 is 10x > than Mb’s

Hb oxygen binding curve

sigmoidal

Mb oxygen binding curve

rectangular hyperbolic

Mb binding site for O2

1 for O2 storage

Hb binding sites

4 binding sites per molecule

low pO2 acts as binding O2 very weakly, but…

as more is bound affinity becomes greater

cooperatively

binding of a ligand at 1 sites affects binding of ligands at another site